This invention relates to a roll for the pressure treatment of a web of material which includes an hollow outer roll and crosspiece extending therethrough with a longitudinal chamber filled with pressure fluid formed between the cross piece and hollow roll, in general and more particularly to apparatus for maintaining a constant temperature in the pressure fluid in such a roll.
A roll for the pressure treatment of webs of material which includes a hollow roll forming the working roll circumference, a cross piece which goes through the hollow roll lengthwise and leaves radial spacing all around from the inside circumference of the hollow roll and protrudes in the lengthwise direction from the hollow roll at the ends, longitudinal seals arranged at the cross piece and extending over a substantial part of the length of the hollow roll and defining a longitudinal chamber located between the inside circumference of the hollow roll and the cross piece in the action plane of the roll, a feed line and a discharge line for pressure liquid which open into the longitudinal chamber, and a temperature setting device for the pressure liquid is described in German Pat. No. 10 26 609. The longitudinal chamber lies on the side of the rolling gap and supports the hollow roll from the inside on a pressurized liquid cushion as if floating. The support is not purely hydrostatic. Rather, an hydrodynamic equilibrium is maintained, in which pressurized liquid is fed to the longitudinal chamber at the feed line and is removed again from the longitudinal chamber at the discharge line.
In many cases not only is a longitudinal chamber formed on the side of the rolling gap filled with pressurized liquid, but the opposite longitudinal chamber which accounts for the remainder of the space between the inside circumference of the hollow roll and the cross piece is also filled. The resulting forces which form the line pressure at the rolling gap are then obtained from the difference of the pressures, taking the effective area of the longitudinal chambers into consideration.
It is also known in such rolls to influence the temperature of the working roll circumference via appropriate temperature control of the pressurized liquid. The feeding and discharging of liquid in such cases is done at opposite ends of the roll so that a flow over its entire extent is obtained. If the requirements as to constant temperature transversely to the web of material or along the roll are stringent, problems arise, however, because a temperature change always occurs along the flow path. Practice has shown that, for instance, in the case of heated rolls, a temperature difference of up to 10.degree. C. can prevail between the ends of the roll if the flow is only in one direction; for many applications of interest, this temperature difference is too high.
In a roll of the type of German Pat. No 10 26 609, it is, therefore, known already to have heated pressurized liquid flowing through the longitudinal chamber located on the side of the rolling gap from one end of the roll to the other in one direction and through the opposite longitudinal chamber in the other direction. The effect on the hollow roll is made up of the effects of the two longitudinal chambers together, and in this manner an equalization of the temperature gradients and a rather good temperature constancy along the roll is obtained. The prerequisite therefor, however, is a roll with two longitudinal chambers through which liquid can flow along the entire length of the roll.
This condition, however, is not always met.
A first example where this condition is not met is the case where the opposite, so-called, leakage chamber is not filled. This is the case, for instance, in what is known as an easy-running roll according to German Pat. No. 27 44 524, in which special precautions are taken in order to avoid hydrodynamic resistances at high operating speed. This includes insuring that no pressurized liquid accumulates in the leakage chamber.
Another example occurs when the longitudinal chamber which is primarily responsible for the generation of the line pressure is located on the side of the rolling gap, but is not continuous over the entire length of the roll. Rather, it is subdivided in the transverse direction so that it forms, for instance, three zones, of which two narrower ones are located at the ends of the roll and the larger one in the center. This can be necessary for influencing the line pressure. Because a continuous flow over the entire length of the roll cannot be generated, special problems as to the uniformity of the temperature arise here.
It is an object of the invention to reduce or compensate for the temperature gradient even in these cases.